T cells may be genetically modified to target antigens expressed on tumor cells through the retroviral insertion of a gene encoding a chimeric antigen receptor (CAR). A CAR is typically composed of a murine antibody- derived tumor-targeted single chain fragment length antibody (scFv) fused to the CD28 co-stimulatory receptor transmembrane and cytoplasmic signaling domains, fused to the cytoplasmic signaling domain of the CD3 6 chain. T cells expressing the resulting CAR gene product subsequently recognize and lyse normal as well as tumor cells which express the targeted antigen. 19-28z is a CAR specific to the CD19 antigen expressed on normal B cells as well as most B cell tumors. Human T cells expressing the 19-28z CAR lyse CD19+ tumor cell lines both in vitro, and in vivo in SCID-Beige mice. Although these data are consistent with the ability of genetic manipulation to overcome tumor cell escape from immune detection, these studies fail to address other potential limitations of this gene-based immune approach. Specifically, prior studies have demonstrated that while genetically targeted T cells are susceptible to inhibition by other factors present in the tumor microenvironment including CD4+ CD25hi regulatory T cells (Tregs) as well as the inhibitory cytokine TGF2. T cells further modified to express the IL-12 cytokine become resistant to these inhibitory factors. Recent studies have demonstrated a remarkable resistance of human effector T cells to inhibition by either cultured autologous Tregs or exogenous TGF2. A clinically relevant syngeneic and immune competent hCD19+ tumor model has been developed in the laboratory utilizing transgeneic C57BL6 murine CD19 knockout, hCD19 knockin (mCD19-/- hCD19+/-) mice to 1) better define the role of the immunosuppressive microenvironment, 2) assess the role of IL-12 secreting genetically targeted T cells in modulating this microenvironment, and 3) study the safety as well as develop and test suicide gene approaches to selectively delete modified T cells following complete tumor eradication. Aim1 of this proposal will test the hypothesis that IL-12 secreting targeted T cells are resistant to prominent suppressive factors present in the tumor microenvironment including Tregs, the inhibitory cytokines TGF2 and IL-10, and PD-1 activation on T cells by PD-L1 expressed within the tumor microenvironment. Aim 2 of this proposal will test the hypothesis that localized IL-12 secretion by targeted T cells will recruit or activate other host immune elements, including natural killer cells as well as anergic TILs, thereby broadening the anti-tumor immune repertoire. Aim 3 of the protocol will study the potential side effects of IL-12 secreting targeted T cells in the immune competent host, and further test a novel suicide gene approach designed to eradicate adoptively transferred T cells following complete tumor eradication thereby enhancing the safety profile of this therapeutic approach. Data generated from these studies will ultimately serve to provide the rationale of utilizing IL-12 secreting tumor targeted T cells in future clinical trials of adoptive immunotherapy in patients with both hematologic and solid tumor malignancies.